<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        li {
            line-height: 60px;
        }
    </style>
</head>

<body>
    <ul>
        <li>1</li>
        <li>2</li>
        <li>3</li>
        <li>4</li>
        <li>5</li>
        <li>6</li>
        <li>7</li>
        <li>8</li>
    </ul>
</body>
<script>
    let liArr = document.getElementsByTagName('li');
    for (let i = 0; i < liArr.length; i++) {
        if (i % 2 != 0) {
            liArr[i].style.backgroundColor = "#cccccc";
        }
        liArr[i].onmouseover = function () {
            this.style.backgroundColor = 'pink';
        }
        liArr[i].onmouseleave = function () {
            if (i % 2 != 0) {
                liArr[i].style.backgroundColor = "#cccccc";
            } else {
                this.style.backgroundColor = '';

            }
        }
    }
</script>

</html>